Historically, the pressurization and ECS needs of most recent military and commercial aircraft have been met by tapping the compressed air energy of the aircraft turbine engines. This was accomplished by providing bleed ports or taps, on the compressor of the engine, typically at the intermediate stage and last stage of the multiple pressure stages of the compressor. In most applications, therefore, there are two pressure taps: one that is used at low power settings on the engine and another at high power settings. For example, at the take-off, climb and cruise conditions of the airplane, the intermediate stage (such as a 5th or 7th stage tap) is adequate to provide the necessary pressure-ratio to pressurize the aircraft cabin: however, at low power settings, as during loiter conditions around an airport, it is necessary to use the last stage tap, or a much higher pressure ratio bleed. These taps have led to inefficiencies of weight, and possibly more importantly, to inefficiencies of engine performance.
Because of these problems, the thrust of this invention is directed at the elimination of the practice of using engine compressor air power for the ECS, air turbine motors, icing protection requirements and other functions in an airplane. Furthermore, the practice has become more unacceptable as the world's fuel shortage problems have come into focus and the price of fuel has increased. Reacting to this, the engine designers have moved the design of their engines towards higher compression ratios and higher fan bypass ratio, so as to make the engines more fuel-efficient. Paradoxically, this has made the engines even more sensitive to "bleed," and it has promoted the present interest in the All Electric Airplane, where the use of mechanical power (to drive generators) is proposed on the grounds that this power extraction method is much less penalizing in fuel than the engine air bleed.
It has also been known in earlier piston-engined aircraft (and in the later turbo-prop aircraft), to utilize engine driven compressors as the energy source for the ECS and pressurization requirements of the airplanes. These engine driven compressors are in fact competitive with the electric motor driven compressors (which are the subject of this invention) since they are also a more energy efficient solution to the problem than bleed air. However, there are problems indigenous to the mechanical compressors that detract from their utilization as a viable source of power for the ECS, de-icing and pressurization needs of the modern airplane. Typically, the mechanical compressors run at extremely high speeds of 35,000 to 60,000 rpm; they sometimes employ gear changes to account for air density/pressure altitude variations: they incorporate electromechanical disconnects to protect the aircraft engine against mechanical failures in the ECS compressor; the compressors are located in the high vibration/high temperature environment of the aircraft engine; and the ECS compressors must incorporate a self-contained lubrication system for the gears and bearings. Finally, a more critical deficiency resides in the fact that an engine-installed compressor requires the routing and installation of expensive, customized ducting in the nacelles, pylons and wings of the airplane, which can be eliminated in the instant invention.
There are several prior art patents that relate to the use of impellers and compressors as means of providing compressed air, but none has the specificity that is the subject of the instant invention. U.S. Pat. No. 2,547,169, issued to W. W. Pagett, discloses a highly mechanically-detailed patent pursuant to a pressure regulating device for monitoring cabin pressure in an aircraft. It describes also a rotary compressor with a plurality of stages, having means for bypassing and inserting stages of the compressor to compensate for pressure/density changes. It does not, however, relate to two-speed motor compressors, operating on variable voltage/variable frequency nor does it reference the use of inlet guide vanes, IGV.
U.S. Pat. No. 4,015,438 to Kinsell et al. describes an air conditioning system primarily for rail cars or ground air conditioning systems. The system utilizes a motor driven compressor/turbine combination, in which cooling air is expanded through the turbine, while the compressor serves to restore the discharge air to ambient pressure. Another patent, U.S. Pat. No. 3,430,921 to Dewey, describes a mechanical integration of two radial air machines in which a rather unique mechanical design permits communication between the two centrifugal impellers.
As will be seen in the following description of the instant invention, none of the aforementioned inventions address the objectives and implementation aspects of a novel motor-driven compressor system (operating on a variable voltage/variable frequency system) in terms of meeting the requirements of an energy-efficient ECS in modern aircraft. From the foregoing, it can be seen that it is a primary object of the present invention to provide an ECS system that includes a motor driven compressor that operates on VV/VF power, and novel means for maintaining pressurized power over variable altitude and variable engine speed conditions of an aircraft.
It is also an object of this invention to provide an ECS system that delivers cooling air on the ground by expanding motor driven compressor pressurized discharge air and expanding it through a turbine (mounted on the motor shaft) after it has been passed through a precooler.
It is also an object of the present invention to provide an ECS system characterized by a constant pressurization capability, from low to high altitude, by using a variable-speed motor and an advanced compressor design with IGVs.
A further object of this invention is to provide an ECS system for aircraft which maintains pressurization levels, during conditions of idle-descent let-down, by the use of a second, supercharging, compressor mounted on the same shaft as a primary compressor.